Re: [manifest] Updating is under/incorrectly specified (#384)

> We have to have a stable URL for locating the manifest resource for describing a site

OK, I chatted with @sicking about this and he has a suggestion...

If we can't guarantee that the manifest URL is stable then an alternative is to use the start_url as the stable URL instead. We can update the manifest whenever the user visits the start_url (which happens whenever they launch the app from its launcher) - if a new manifest URL is linked from the page at the start_url when it is loaded, then we can update the manifest URL for the site and download the new manifest.

@sicking suggests that we should also periodically fetch the start_url, parse its HTML and follow its manifest URL in order to update the manifest for a site, even when the user doesn't visit it. I'm not sure whether that part will work.

Theoretically you could probably still also change the start_url as long as the manifest is still linked from the old start_url and you don't try to change both at the same time, or the old start_url redirects to the new start_url, but that might get a little bit hairy. We don't think sites change their start_url very often anyway...

One slight issue with this is that the default start_url is currently defined as the document URL an app is installed from, which could be different for every install. Updating the manifest then relies on every page of the app being updated with a new manifest URL and never disappearing.

For this reason I'd like to suggest that either the start_url become a mandatory field, or the default start_url be the root of the origin.

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https://github.com/w3c/manifest/issues/384#issuecomment-119706439